A capacitance type physical quantity sensor for detecting physical quantity is disclosed, for example, in Japanese Patent Application Publication No. H11-326365 (i.e., U.S. Pat. No. 6,151,966). The sensor includes a movable electrode having multiple comb-tooth electrodes and a fixed electrode having multiple comb-tooth electrodes. The sensor further includes a movable portion having a massive portion and the movable electrode integrally formed with the massive portion. When the physical quantity is applied to the sensor, the movable portion is displaced in accordance with the physical quantity. At that time, a displacement direction of the movable portion is perpendicular to a detection surface of each of the movable electrode and the fixed electrode. The detection surface of the movable electrode faces the detection surface of the fixed electrode so that a capacitor having a capacitance is formed between them. As a distance between the detection surfaces becomes shorter, the capacitance of the capacitor becomes larger, and as the distance between the detection surfaces becomes longer, the capacitance becomes smaller. Accordingly, the physical quantity is detected on the basis of a capacitance change caused by a distance change.
However, in the above physical quantity sensor, when the movable portion (i.e., the movable electrode) is displaced, damping effect works in a squeezing direction (i.e., the displacement direction of the movable portion) between the detection surfaces of the movable and the fixed electrodes because of viscosity of fluid (i.e., gas, liquid or the like) disposed between the detection surfaces. Accordingly, the displacement of the movable electrode becomes small because of the damping effect, so that the capacitance change of the capacitor also becomes small in accordance with the displacement of the movable electrode. Therefore, sensitivity of the sensor is reduced. Specifically, as the distance between the detection surfaces is shorter, the damping effect much affects the displacement of the movable electrode, i.e., the displacement is much reduced. Therefore, in this case, the sensor cannot detect fine physical quantity.